The present invention relates to programmable logic devices (PLDs). More particularly, the present invention relates to a PLD with a transceiver and a reconfigurable phase-locked loop (PLL) circuit.
A PLD is a flexible device that includes programmable function blocks (also called IP blocks in the industry) programmably connected via a programmable interconnect structure. Typical function blocks include logic blocks, processor blocks, signal processor blocks, PLL blocks, memory blocks, input/output blocks, etc. A user can select which blocks to connect, and the functionality of each block, depending on the particular job the PLD is to perform. In this manner, a PLD is a low-cost and flexible solution to a wide variety of system requirements.
Exemplary PLDs include field programmable gate arrays (FPGAs) such as STRATIX™ devices, APEX™ devices, and FLEX® devices; complex programmable-logic devices (CPLDs) such as MAX® devices; and embedded processors such as EXCALIBUR™ devices, all from Altera Corp., San Jose, Calif.
A PLL circuit is a circuit that generates an output signal based on an input signal. A typical PLL circuit includes a reference divider, a feedback divider, a comparator, a charge pump, a loop filter, and an oscillator. The output signal is then a function of the input signal and a ratio between the reference divider and the feedback divider. In a reconfigurable PLL, the values in the dividers are programmable, which allows the PLL to generate a very wide variety of output signal frequencies that can be changed during normal system operation.
One type of function performed by some PLDs is a transceiver function. A transceiver refers to a circuit element that receives and input signal and/or generates an output signal. For the wide variety of potential systems that use PLDs, a correspondingly wide variety of input signal types are provided as inputs to the transceiver. In many instances, numerous external components must be provisioned so that the input signal to the PLD conforms to a particular type of signal. Similarly, a correspondingly wide variety of output signal types may need to be provided as inputs to other system components from the output signals from the PLD, which in many existing systems may also require numerous components between the PLD and the other system components.
There is a need for a PLD that more flexibly responds to the wide variety of potential input signals, and that more flexibly generates a wide variety of potential output signals, without requiring dependence upon external components.